title: Blood oxygen level-dependent activation of the primary visual cortex predicts size adaptation illusion.
abstract: In natural scenes, objects rarely occur in isolation but appear within a spatiotemporal context. Here, we show that the perceived size of a stimulus is significantly affected by the context of the scene: brief previous presentation of larger or smaller adapting stimuli at the same region of space changes the perceived size of a test stimulus, with larger adapting stimuli causing the test to appear smaller than veridical and vice versa. In a human fMRI study, we measured the blood oxygen level-dependent activation (BOLD) responses of the primary visual cortex (V1) to the contours of large-diameter stimuli and found that activation closely matched the perceptual rather than the retinal stimulus size: the activated area of V1 increased or decreased, depending on the size of the preceding stimulus. A model based on local inhibitory V1 mechanisms simulated the inward or outward shifts of the stimulus contours and hence the perceptual effects. Our findings suggest that area V1 is actively involved in reshaping our perception to match the short-term statistics of the visual scene.
authors.affiliation: Scientific Institute Stella Maris, 56018 Pisa, Italy, Institute of Neurosciences, National Research Council, 56124 Pisa, Italy, Department of Neuroscience, Psychology, Pharmacology, and Child Health, University of Florence, 50121 Florence, Italy, and Department of Translational Research on New Technologies in Medicine and Surgery, University of Pisa, 56126 Pisa, Italy.
authors.forename: Arezoo
authors.initials: A
authors.lastname: Pooresmaeili
authors.forename: Roberto
authors.initials: R
authors.lastname: Arrighi
authors.forename: Laura
authors.initials: L
authors.lastname: Biagi
authors.forename: Maria Concetta
authors.initials: MC
authors.lastname: Morrone
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D015350:Contrast Sensitivity / Q000502:physiology; D005260:Female; D005556:Form Perception / Q000502:physiology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D009903:Optical Illusions / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology; D012858:Size Perception / Q000502:physiology*; D014793:Visual Cortex / Q000502:physiology*